Extraction method



EXTRAGTION METHOD Fiea June 5, l1945 COLUMN -exrza erle/v- .conan/vPatented May 14, 1946 I Ex'raAc'rIoN METHQD 'Daniel E. stilles,Plainfield, N. J., assigner to Standard Oil Development Company, a cor'-poration of Delaware Application June 5, 1943, Serial No. 489,779

claims. (c1. 19e- 13) yThe present invention relates to methods ofseparating by means of a selective solvent, a mixture of liquidcomponents into desired fractions l and, more particularly, it relatesto a liquidliquid extraction process in whicha mixture of liquidcomponents may be solvent extracted to separate and recover valuablecomponents from the mixture, or to improve the originalmixture byremoving certain undesired components therefrom.

Prior to my invention numerous processes were or oleflnic nature whichboil in close proximity .to butadiene and cannot be separated therefromby distillation. My present invention is directed broadly to the conceptof fractionatins.r liquids by selective solvent action, in particularwhere two normally immiscible or partly miscible liquid materials arecontacted. For example, the invention is applicable in such processes asliquid SO2 treatment of lubricating oilsto remove undesired components,liquid phase extraction of HzS from liquid hydrocarbon streams, liquidphase extraction of heavier liquid is dispersed in the lighter liquid inthe bottom section of the tower While in the top section of the tower,the lighter liquid is dispersed in the heavier liquid. I have found thatthis method gives better results.

One object of my present invention is to solvent treat a liquid mixtureof a plurality of components with a liquid solvent to remove undesiredcomponents under conditions obtaining for maximum efliciency.

A more specic object of my invention is to 'provide means for solventextracting hydrocarbon oil, such as lubricating oils, under conditionswhich will result in improvement of the raiilnate and permit the use ofless solvent, for a given number of actual extraction stages, than wouldbe required with single phase operation or by the so-called split phaseoperation.

Other and further objects of my invention will appear from the followingmore detailed description and claims In the accompanying drawing, I haveshown in Fig. I, in vertical section an apparatus in which onemodification of my invention may be'carried into practical effect, andin' Fig. III I have shown a. further modification representing a secondpreferred embodiment of the said invention. In theviews, similarreference characters refer to similar parts.

Referring in detail to the drawing l represents inv either Fig I or 1I asolvent extraction column, divided into an upper and lower separatedsection by means of partition plate I9, and in which butadiene fromliquid C4 streams, and the like.

It is the aim of 'my present invention to increase the eiliciency ofsuch processes.

In the prior art there are solvent treating processes involving theso-c'alled split phasei. e.. maintaining an interface ofthe heavierphase in the central portion of the extraction column. In this type ofprocess, the lighter liquid is fed to the bottom of a verticalextraction tower while the heavier liquid is fed to the top of thetower. The

liquids flow countercurrently through the tower. In the bottom of thetower, the lighter liquid is dispersed lnthe heavier liquid and in thetop section of the tower the heavier liquid isdispersed in the lighterliquid. As indicated inA the middle' of the tower there is' an interfaceof the heavier means are provided for contacting two immiseible or onlypartly miscble liquids as where, for example, lubricating oil is causedto flow in countercurrent flow to a selective liquid solvent for cer-ltain vcomponents ofthe oil, such as liquid SO2." y

The lubricating oil, in the example'I have chosen to illustrate myinvention, to be treated representduced at near the top of the towerthrough inlet pipe I0. In the method illustrated in Fig. reversal of thephases is accomplished as follows: In the upper section. above plate I9,the solvent is the continuous phase, while in the lower section thehydrocarbon is the continuous phase, and I achieve phase reversal of theliquids moving countercurrently,y across partition plate'. I9, in' thetower, by controlling the rate of withdrawal of the. solvent from theVupper section of the tower through pipe 2l into'the lower section,coupled with continuing the rate of withdrawal of sol- Y vent from thebottom or the tower through drawoit pipe l2. .The ilcw rate of liquid inpipe 20 is controlled by valve 22 responsive to liquid level controldevice 3l and the level In oi the extract at the bottom of the lowersection is controlled by valve Il operating in response to level controll mechanism Il. Thus, the hydrocarbons entering' at 5 in Fig. I becomethe continuous phase in the section or the tower belowplate I9,flowcountercurrently upward against the downiiowing solvent and enterthe upper section through pipe 24. In the upper section the hydrocarbonbe-` comes the disperse phase, In the upper section the hydrocarbonspass mostly through the perforations or pierced plates 15a while in thelower section the dispersed solvent iiows through the Vperi'orations o!pierced plates I5. To build up a static pressure oi' the solventin thelower section, I provide the plates I5 with dams I1. In; the

upper section projections ila are turned downwardly. In Fig. I, thearrows, therefore, indi- Y cate, in the upper section the ilow orsolvent i. e.

S01, while they indicate the flow of hydrocarbon in the lower section.

In Fig, II, the same phase reversal takes place, i. e., the hydrocarbonsentering at 5 form the continuous phase. below plate I9 while above I9,the heavier solvent phasel ls the continuous phase. In thismodification, I achieve phase reversal across plate I9, by hydraulicmeans. T0 this end,

liquid iiows from the upper section through 20 and 20a forming togethera, U bend, into the lower section of the column I and following thisflow the solvent is discharged as the dispersed phase into thecontinuous hydrocarbon phase. Aconnection 2lb serves to prevent asiphoning effect. Except as indicated, the operation of the device ofFiglListhesameasthat ofFig. I. In both iigures, ramnate is recoveredthrough line 40 and this raiiinate may be treated to remove solvent inknown manner and otherwise refined. For simplicity and in the interestof clarity, I have limited the showing in the drawing to the heart ofthe invention, omitting conventional after-treatingl tion column whilethe lighter or lower density liquid is dispersed in the heavier liquidforming the continuous phase, in the upper part of the said tower, therebeing therefore a phase reversal at an intermediate point in said tower.

In Hg. I, I have previously indicated automatie mechanism forcontrolling the liquid level Li in the upper section of tower i and Lnwhich is the level of the accumulated solvent in the bottom of thetower. A mechanism for controlling the rate of liquid withdrawalsuitable for use here is the so-called duo-gravity type" liquid level'saturation or emciency of the solvent. Similarly.

the material to be extracted is dispersed in the portion ofthe extractoradjacent to its withdrawal point, which exposes maximum extractablesurface and permits maximum cleanup or degree of extraction of thecomponents which it is desired to extract. Conversely, the solvent isthe continuous phase at that point in the system where it is the leastsaturated, and the material to be extracted is the continuous phaseinthat region where it has the highest concentration of extractablematerial. The above principles obviously contribute to both maximumetliciency of the solvent and maximum percentage removal oi extractablematerial in a given number of extraction stages. l

2. A lower quantity of solvent is required for a given amount ofundesired material removed and where the solvent withdrawn through line42 is recycled for further use, as ofcourse it would be in commercialoperation. the amount of solvent recycled would be from l0 to 30% lessthan in the normal solvent treating process, where the solvent is the.continuous phase as it leaves the extraction tower.

. It will be understood that my invention embraces solvent treating whenthe solvent is the lighter or of lower density than the material to betreated in which case the extract would be withdrawn through I0 whilethe railinate would contact a selective liquid solvent in an elongated vvertical treating zone, by lforcing the solvent into one end oi' thetreating zone asja continuous phase, simultaneously forcing the liquidmaterial to be treated into the other end of the treating zone as acontinuous phase, the solvent and material to be treated being oi'diilerent densities, permitting the solvent and liquid material to iiowcountercurrently to each other in the treating zone. and controlling theiiow rate of liquids and liquid levels in the treating zone so as tocause the solvent vto be the disperse phase at the end of the treatingzone furthest removed from its point of introduction therein andsimilarly causing by the same means the liquid to be treated to be thedisperse phase at the' end of the treating zone furthest removed fromits point of incontrol device, a device whose structure and modetreating zone and the hydrocarbon oil being in troduced into the bottomof the tower.

4. The method of claim l in which the solvent is the continuous phase inthe portion of the treating zone nearest its point of introduction andthereafter undergoes phase reversal at near the vertical middle of thetreating zone to become the disperse phase in the portion of thetreating zone nearest its point of withdrawal.

5. In the solvent extraction of a liquid mixture containing a pluralityoi' components with phase therein, causing the two' liquids to flowcountercurrently in said extraction tower, inter- 10 tom of said tower.

rupting e free ilow oi the liquids in said tower at an in mediate point,adjusting the rate of ow of the liquids within said upper and lowersections and across said point of interruption so that the heavierliquid forms a dispersed phase in the lower section and the lighterliquid forms a dispersed phase in the upper section, and withdrawing thelighter liquid phase'from the top and the heavier liquid phase lfrom thebot- DANIEL E. STINES.

